SCEC Award Number 13056 View PDF
Proposal Category Collaborative Proposal (Special Fault Study Area)
Proposal Title Using Mechanical Models to Test Community Fault Model Updates to the Western Transverse Ranges Region, CA: Application to the Ventura Special Fault Study Area
Name Organization
Scott Marshall Appalachian State University Gareth Funning University of California, Riverside Susan Owen National Aeronautics and Space Administration Jet Propulsion Laboratory John Shaw Harvard University
Other Participants
SCEC Priorities 4, 1, 2 SCEC Groups USR, Geodesy, SDOT
Report Due Date 03/15/2014 Date Report Submitted N/A
Project Abstract
The recognition of the greater Ventura region as a Special Fault Study Area (SFSA) has largely been driven by recent work suggesting a significantly greater seismic hazard than was previously recognized for the region. Recent versions of the SCEC Community Fault Model (CFM) for the western Transverse Ranges have been tested using geodetically-driven mechanical models [Marshall et al., 2008; Marshall et al., in review]. In order to test the updated fault geometries posed by Hubbard et al. [in review] and to better characterize current fault slip rates and slip distributions in the Ventura basin region of the Transverse Ranges of southern California we are working to create a numerically-stable three-dimensional Boundary Element Method (BEM) fault mesh incorporating the new fault geometries proposed by Hubbard et al. [in review] for the greater Ventura region. The models will be used to calculate the likely long term slip rates and slip distributions on the modeled surfaces. We will also use the models to determine if the current geodesy data is capable of distinguishing between the CFM 4.0 geometry and the fault geometry proposed by Hubbard et al. [in review]. Given the late funding of this project due to the federal government sequester, the project has been extended for a second year, thus, we will report preliminary results at this stage.
Intellectual Merit This project contributes to the understanding of crustal deformation in southern California by using a novel three-dimensional mechanical modeling approach to simulate both interseismic and long-term deformation. A primary goal of the Ventura Special Fault Study Area (SFSA) is to determine the most likely fault structure for the region, and this work contributes to this effort by directly testing an updated fault system geometry for the greater Ventura region. This work will directly test whether any geologic/geodetic rate discrepancies exist in the western Transverse Ranges, and if the geologic slip rates are more compatible with the old CFM4.0 fault geometry or the updated fault geometry of Hubbard et al. [in review]. Our modeling approach utilizes the CFM geometry and offers a quantitative assessment of the ability of the CFM to reproduce variations in slip and interseismic deformation in southern California. Furthermore, a product of this study will be a significantly updated fault model, which will be included in a future release of the SCEC CFM.
Broader Impacts This work has fostered collaborations between researchers at the Jet Propulsion Laboratory, the University of California Riverside, Harvard University, and Appalachian State University. At Appalachian State University, PI Marshall has now begun training undergraduate students in GPS processing, dislocation modeling, and stress/strain theory. Marshall is currently training a Ph.D. student at the University of Massachusetts on GPS processing, and working with two undergraduate geology students at Appalachian State University. One student is writing a dislocation modeling code, while the other is doing GPS time series processing to determine seasonal aquifer motions. These efforts are aimed to produce future researchers that are better prepared for graduate school and the research community. Also, by training undergraduate students, interest and understanding of earthquake science is promoted. The results of this work will have an impact on society by more accurately characterizing the slip rates of faults, which in turn leads to improved seismic hazard estimates.
Exemplary Figure Figure 3. A) Reverse slip rates and B) net slip rates along the South San Cayetano-Ventura-Pitas Point fault system of Hubbard et al., [in review]. In B) the net slip vector (black arrows) is mapped onto the hanging wall of the fault. The view is oblique and to the southeast (refer to UTM axes). Note that the nearly horizontal ramp section causes slip rates to decrease dramatically locally. In the near surface, the fastest slip rates are near the Ventura Avenue anticline at the coastline near the city of Ventura. The apparent missing fault surface towards the left portion of the image is the San Cayetano fault, which is included in the models, but not shown here.